Why ball bearing mains?

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Dances with Shrapnel said:
Clearly there are some trade offs as the roller bearings have roughly 50% greater load bearing capacity than comparable ball bearings. What we do not know is the difference in bearing behaviour beyond the recommended limits. As an example, catalog information for roller bearings recommends consulting with bearing manufactures when greatly exceeding allowable angular misalignment whereas single row deep groove ball bearings seem to have a hard limit for angular misalignment.
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NJ306E dynamic load rating 11600lbs static load rating 10800lbs

6306 dynamic load rating 7500bs static load rating 4000lbs

NJ306E Angle of Misalignment 3-4minutes

6306 Angle of Misalignment 5-10minutes


Edit: The range on the misalignment figures is to cover the range of bearing sizes. They don't list each bearing individually like load ratings.
Edit: I changed the load rating because the figures I used were not for the E extra duty bearing, they are now.


FAG Catalog: (For Deep Groove Ball Bearings)
Misalignment impairs the smooth running of the balls, induces additional stresses in the bearing and consequently reduces the bearing life. In order to control the additional stresses only small values of misalignment - depending on the load - are permissible for deep grove ball bearings.
 
rpatton said:
FAG Catalog: (For Deep Groove Ball Bearings)
Misalignment impairs the smooth running of the balls, induces additional stresses in the bearing and consequently reduces the bearing life. In order to control the additional stresses only small values of misalignment - depending on the load - are permissible for deep grove ball bearings.
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Thanks for the specifics and yes, that sums it up nicely.
 
The 53% balance factor is bullshit if you want to rev a commando motor. It is obvious that the hole in the bob weight is an after thought. All you have to do is tap the hole and fit a well secured steel plug.
 
acotrel said:
The 53% balance factor is bullshit if you want to rev a commando motor. It is obvious that the hole in the bob weight is an after thought. All you have to do is tap the hole and fit a well secured steel plug.
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Here we go again. One small step for man, and one step backwards for technology.

This has been debated ad nauseum.

Off topic and way off the mark.
 
It is not off topic. If you rev a crank with a 53% balance factor, it must do damage - be told ! That is why every twin cylinder motor that has ever been raced in Australia since at least the 50s has had the balance factor changed to suit the rev range at which it was to be used. I will guarantee that when a Norton crank is revving out of balance at 7000 rpm, the bolts are stretching, and the bearings are loaded out of alignment. If it is in balance the shaft doesn't bend so much, and because the forces are less when the crank vibrates you don't shit the cases when you use bearings that don't self-align. It is not rocket science to decide how you want to use your commando and balance the crank to suit.
The very first thing that I did when I built my 850 motor was rebalance the crank, and I am still afraid of it even though the motor only vibrates when it is idling. I built the Seeley around 1978, and did not race it until 2003 because that ridiculous crankshaft was in it. I still wouldn't race it at Phillip Island. I can imagine what it would be like halfway down the long front straight doing over 130mph and knowing what is happening down below.
The only reaon I ever persevered with my short stroke 500cc Triumph for 12 years, was that it had the billet crank with the short stroke, and was almost impossible to destroy if you didn't rev it over 10,500 rpm. I've had too many high speed crashes, and I don't want another at age 71.
 
acotrel said:
It is not off topic. If you rev a crank with a 53% balance factor, it must do damage - be told ! That is why every twin cylinder motor that has ever been raced in Australia since at least the 50s has had the balance factor changed to suit the rev range at which it was to be used. I will guarantee that when a Norton crank is revving out of balance at 7000 rpm, the bolts are stretching, and the bearings are out of alignment. If it is in balance the shaft doesn't bend so much, and because the forces are less when the crank vibrates you don't shit the cases. It is not rocket science to decide how you want to use your commando.
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Beg to differ dear acotrel; way off topic and way off the mark...again, but I'll give you credit for consistency. I cordially invite you to re-read the topic title.

Bikes since the 50's?...........give me a break. When were the isolastic Commandos introduced???? Old bikes had to run higher BF to protect frame and rider and they did this by compromising the balance factor. Again, higher balance factors are artifacts of the solid engine mount days for a Norton big twin.

You have consistently failed to provide a shred of relevant evidence to support your assertion; those articles you do reference pertain to solid mounted engines and of course they had to raise the balance factor. We all know that as common knowledge. To me, your vernacular use of the term "bullshit" is very telling as it is on an emotional (non-technical) level and to me indicates the level of technical background supporting your assertions. Bring something substantial and substantiated to the table if you want to get technical.

As for your guarantee; really bold statement there. :roll: :lol: Let me clue you in on a little something you may not be aware of; the bolts are stretching, and the bearings are out of alignment at any rpm regardless of the balance factor used. It is a matter of degree and you should have known this. The goal is to minimize the magnitude of the bending moment reversals. I now see that this concept has clearly gone over your head.

I suggest you start a new thread titled "alternate universe cry balance factor thesis" or something like that and stop muddying up topics.

Again, bring something other than "bullshit" to the table and something that is substantial and substantiated if you want to get technical.
 
'The goal is to minimize the magnitude of the bending moment reversals.'

I suggest that when the crank is doing 7000 rpm, the flywheel probably has the crank stretched open at the flanges next to the side of the weight away from the journals and the bolts are under fairly constant load. If you are using the bearings too dampen out the reversals, it is the wrong use. But if the crank is balanced correctly the reversals should not happen so much because all you are doing is swinging a heavy weight and using its inertia to dampen out vibration.
I know you guys probably worship Peter Williams and believe in the commando design - I don't ! - Commandos are rubbish. They should have all been fitted with billet cranks, and I wouldn't have been nervous about racing mine.
 
According to a friend of mine who live near Bendigo in Northern Victoria, there is a guy in that town who was fitting double row ball races to both side of cranks in standard commandos. Destroyed a few crankcases on his customers bikes. Too rigid !
 
I've just returned from my Peter Williams shrine where I was dismayed to find several incense sticks had been snuffed out :roll: - WTF?

@acotrel - As best as I can tell nobody has suggested the bearings are being used to "dampen out the reversals" far from it so this bit of blathering and blating about balance factor is off topic. The bearings are there to support all the forces due to combustion and eccentric loads.

Based on your explanantion it is apparent that you have this vision of what you think is going on but it is not complete. You need to look at the kinematics and dynamics of the crank/rod/piston assemblies in various angular displacements to get a grip on what is happening. Motoring the Norton engine, loads are quite different at TDC and BDC and 90/270 degrees; add combustion chamber pressures and things get pretty complicated. There are piston and rod acceleration and decceleration forces that need to be dealt with.

Doing a summation of the bending moments about a crank at TDC, BDC and 90/270 will paint a picture for you.

As for us guys worshiping Peter Williams, he was certainly a part of the early history and I for one respect him for what he did and what he achieved but I don't worship him so another one of your concepts is wrong .......again.

As for you stating Norton Commandos are rubbish, I now see the unbiased unsubstantiated technical position you are coming from. :roll:
 
Ugh, the shade tree in Arkansas requests review of reports of cracked in half crank cases with their BF if possible, for a feel of which BF might survive higher rpm. The real issues are, that everybody can't win a race nor be correct on best BF per bearing type per case type and crankshaft with rods its pistons installed in rubber or solid frame. If Peels rollers blow up I'm Blaming the guy nicked named Dances with Shrapnel for making me do it that way this time around.
 
How much do you believe the flywheel moves off centre and returns on every rev of a standard commando motor ? What is the amplitude and frequency of the vibration ? I suggest that the flywheel moves until the forces balance, and the vibration amplitude is well within the bearing tolerance at the revs to which the crank is balanced. If the crank is out of balance at any part of the usable rev range, the extra force is destructive , but if the out of balance occurs only at low revs , and not higher up the rev range, the forces involved are less. If you constrain the crank by using close tolerance roller bearings, I suggest you risk concentrating the stresses at the stress raisers on the crank, or cracking the crankcases , or destroying the bearings themselves. Fatiguing the bolts holding the shaft together is always a risk.
If you want a commando to go fast, buy a Weslake motor for it.
 
acotrel said:
According to a friend of mine who live near Bendigo in Northern Victoria, there is a guy in that town who was fitting double row ball races to both side of cranks in standard commandos. Destroyed a few crankcases on his customers bikes. Too rigid !
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Yes, this sounds plausible if you can find a double row ball bearing to fit the 72mmX19mmX30mm bearing envelope. A quick look in the catalog indicates none. He could have done some machining and modifications to the cases to fit some other bearing but then all bets are off.

I can see a double row ball (or roller) being incredibly stiff.

What double ball could this fellow have possibly fit in a 72mmX19mmX30mm? The closest I can find is two side by side but the fellow would have had to sleeve them to fit the cases and the load rating on the bearings were only a fraction of the NJ306E or N6306 ball bearing. Furthermore, loading on the bearing bosses from the "half width" outer races would have certainly been a disaster.
 
I suggest you should fit a commando motor with weights for the big end exacvtly matching the rod and piston weight. Put it in an open jig using superblend bearings, then spin it to 8000rpm and shine a strobe light on it. Another exercise could be to mount load cells on the main bearing mounts, and use a computer to assess the loads at 8000 rpm using high and low balance factors.
 
I once had a double row ball bearing which would fit the timing side of a pre-unit Triumph, I was thinking of using it, but was talked out of it. If the crank cannot flex it can break. And I never used roller bearings on both sides of the triumph crank, always a ball on the timing side.
 
I don't even know w ho that was fitting close tolerance bearings to commandos. But some of the bearing companies have a 'special list'. My Triumph was fitted with unobtainable bearings when I bought it. I reground the crank to fit standard main bearings.
 
Our cranks always out of balance but vary on which radian vector the most.
I believe that the crank mostly stays aligned till some threshold hit then suddenly slings into jump rope damage zone rather than a steady increasing deflection rate. Only way I can think of to monitor this short of blow up is to run a witness screw up to flywheel rim then back off a tad then work up rpms in stages and suck out bolt and look before next rpm stage. Small-ish bolt with soft-ish material or tip of course. Might work for cam shaft sling too.

Another thing to think about on rod area failures is if the crank bowing in middle binds on the big end shells to pop the bolts before just plain piston jerks would.

Here's a vibe vs rotation device I learned lesions on but we called em whirrly gigs

[video]http://www.youtube.com/watch?v=8cEcrHTMbY0[/video]
[video]http://www.youtube.com/watch?v=JRU7-ZrCdrA[/video]
[video]http://www.youtube.com/watch?v=xQ9lnF-K2Ko[/video]
 
acotrel said:
I suggest you should fit a commando motor with weights for the big end exacvtly matching the rod and piston weight. Put it in an open jig using superblend bearings, then spin it to 8000rpm and shine a strobe light on it. .
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I suppose you realise that what you are advocating here is a 100% balance factor ???!!!
Care to explain the purpose of this exercise though ?

This would transfer 100% of the vibes into the fore-and-aft plane.
Make it a real shaker, in a way seldom experienced by any riders.
And probably a real frame breaker, since frames haven't been developed to resist such heavy shaking in this direction, preferring to split the shaking into up-and-down AND fore-and-aft shaking in the 50%-50% range.

P.S. We still think you seem to have this odd notion that parallel twin engines with heavy reciprocating pistons/rods can be 'perfectly' balanced mechanically with some nirvana type BF, and other BFs will be mechanically destructive to the engine ??!!

PPS My veteran early Triumph (single) had a twin row ball bearing on the drive side, OF THE SELF ALIGNING TYPE.
This requirement has been known for 100+ years then...
 
Rohan even if Alan/acetrel math is off - he's not off his rocker to run with 100 BF, but I am so want to try 110% and see whose beliefs to follow. Peels moving along so someday data log kit to pass around and see what it says various BF's feels like to engine, frame or pilot. What I want most to know is how the rear edge patch feels it.
 
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